The Search for R&D Spillovers

R&D spillovers are, potentially, a major source of endogenous growth in various recent "New Growth Theory" models. This paper reviews the basic model of R&D spillovers and then focuses on the empirical evidence for their existence and magnitude. It reviews the older empirical literature with special attention to the econometric difficulties of actually coming up with convincing evidence on this topic. Taken individually,, many of the studies are flawed and subject to a variety of reservations, but the overall impression remains that R&D spillovers are both prevalent and important.